This invention is directed to a method for assaying a drug in tissue. In particular, this invention is directed to a method for assaying a photosensitizing drug in tissue rapidly through the use of fluorescence.
One known treatment for illnesses such as carcinomas and tumors is PhotoDynamic Therapy (PDT). PDT is presently used as primary or adjunctive treatment for benign or malignant tumors. PDT is based on activation, by light, of the photosensitive drug that is in the patient. The treatment involves the introduction of a photosensitive drug into a patient. Typically, the drug is disproportionately concentrated in the target abnormal cells. Such concentrating of the photosensitive drug causes a photosensitization of the patient. In particular, the target abnormal cells are photosensitized more than normal cells.
Accordingly, a source of light is shone at the patient, usually locally directed at the tumor composed of target abnormal cells. The light is tailored to the drug in order to cause a response of the drug to the light. The response of the drug, generally a chemical activation, causes a cascade of events that eventually results in the destruction of the tumor, often by the disruption of the target abnormal cell.
PDT can be given on an ambulatory basis and is often non-invasive. As such, the therapy can significantly reduce the high cost of more traditional treatments and eliminate the long term and often disabling side effects associated with such traditional treatments as radical surgery, radiotherapy, and chemotherapy.
PDT requires the concerted action of a sensitizing drug and an activating light. Neither component alone, as used in PDT, can cure the tumor or harm the healthy tissue. However, with the two components together, the technique powerfully destroys tumor cells selectively. There has been extensively development of technological improvements in both light sources and novel photochemical sensitizers such that commercially available high power compact lasers are used with drugs with improved tumor tissue to healthy tissue selectivity. Further, drugs having shorter half lives are continuing to be developed in order to minimize the time a patient is hyper photosensitive. Such photosensitivity often prevents a patient from outdoor activity because of extreme sensitivity to daylight.
Clinically, the PDT treatment comprises giving a particular chosen photosensitizing drug that is usually injected into the patient. A given delay time period specific to the particular drug is allowed to elapse. The time delay period allows the drug to reach the tumor tissue for light activation. The selective retention of the drug in the tumor tissue, as compared to healthy surrounding tissue, allows the eradication of the tumor tissue with minimal damage to healthy tissue. However, the dose of the drug must be carefully monitored in order to prevent the normal cells from developing a concentration of the photosensitive drug that would photosensitize such normal cells to the light dose. Similarly, the light dose must be set high enough to cause the target abnormal tumor cells to be destroyed with minimal damage to normal cells.
Each patient has an individual metabolic rate, body mass, fluid content, and cellular dynamics such that the concentration of the photosensitizing drug in the patient cannot be accurately determined without actual measurement. The concentration of the photosensitizing drug in the tissue is a reliable indicator of the amount of drug that the cells have taken up. The cells take up each particular drug up to a certain known threshold concentration for each particular drug. Above a certain known maximum concentration for each particular drug, the concentration of the drug is too high in the normal cells, thus causing unacceptable damage to normal cells. The tissue level therefore is an accurate indicator of when the amount of photosensitizing drug is correct for PDT.
Accordingly, the total content of the photosensitizing drug in the patient's tissue must be determined in order that the dose of light be calculated for each patient for a given particular drug. However, current wet chemical or chromatographic techniques for assaying the content of a drug in tissue takes too long for effective PDT use. The concentration of drug can easily change considerably in the time it takes to assay by conventional techniques. Furthermore, the conventional assaying techniques are expensive, demanding extensive laboratory and technical personnel support.